Difficult Creek

Occurrence, Inactive

Commodities and mineralogy

Main commodities Au; Cu; Zn
Ore minerals chalcopyrite; gold; pyrite; sphalerite
Gangue minerals anhydrite; barite; calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale KN
Quadrangle map, 1:63,360-scale A-8
Latitude 60.151
Longitude -152.875
Nearby scientific data Find additional scientific data near this location
Location and accuracy The occurrence located on a small ridge at an elevation of 1,850 feet overlooking Difficult Creek, it is in NE1/4 of section 26, T. 1 N., R. 20 W., of the Seward Meridian. Difficult Creek drains into Tuxedni Bay which is on the west side of Cook Inlet. This location is accurate to within 300 feet.

Geologic setting

Geologic description

The Difficult Creek occurrence is within the lower Jurassic Talkeetna Formation, an approximately 2,575 meter thick sequence of volcanic and volcaniclastic rocks (Determan and Hartsock, 1966). The volcanic section near the prospect is structurally bounded on the west by the Bruin Bay Fault, a major fault system traceable for over 500 kilometers. On the east, the volcanics are unconformably overlain by upper Jurassic marine sediments (Determan and Hartsock, 1965). The Talkeetna Formation is intruded by rocks of the Aleutian range -Talkeetna Mountain plutonic belt approximately 23 km southwest of the prospect. These intrusives which consist dominantly of coarse-grained quartz diorites and quartz monzonites have been dated between 175 and 145 m.y. (Steefel, 1987).
At Difficult Creek, the Talkeetna Formation has been divided into three major groups (Steefel, 1987). The lowest group consist of purple and green andesite flows and breccia which locally show well-developed pillows. The middle group that host the mineralization, consists of coarse-grain felsic breccias, reworked volcaniclastic rocks, crystal tuffs, and dacite flows. The upper group consists of polymictic andesitic breccias and conglomerates with minor amounts of andesitic flows.
The mineralization consists of stratiform massive sulfides layers and lens which contain pyrite, chalcopyrite and sphalerite. There are no published assay results for this occurrence. William Ellis (personal communication, 1999) speculates that this occurrence is a Kuroko type massive sulfide deposit.
Geologic map unit (-152.877228378645, 60.1503945488292)
Mineral deposit model Kuroko massive sulfide (Cox and Singer, 1986; model 28a).
Mineral deposit model number 28a
Age of mineralization Jurassic massive sulfide.
Alteration of deposit The Difficult Creek occurrence has alteration characteristics of a Kuroko type massive sulfide deposit that includes sulfate alteration, and silicification.

Production and reserves

Workings or exploration The occurrence was discovered by Anaconda Minerals in 1982 as part of a exploration program at the Johnson River prospect. To date there has been detailed mapping, stream and soil geochemical surveys, and surface trenching and sampling. No assay results are available.
Indication of production None

Additional comments

This occurrence is owned by Cook Region Native Association.

References

MRDS Number 10307712

References

Steefel, C.I., 1987, The Johnson River prospect, Alaska; Gold rich sea-floor mineralization from the Jurassic: Economic Geology, Vv. 82, p. 894-914.
Reporters Jeff A. Huber (Anchorage)
Last report date 4/15/1999